A colossal space monster materialized in a city and commenced its rampage, sending people fleeing in terror. Among the panicked crowd were five high school students: En, Kai, Shin, Yoku, and Ryu. Unable to escape, they dashed into a nearby parked patrol car. As the monster closed in on them and they resigned themselves to death, the patrol car glowed with a blue-white light and vanished into a mysterious space, taking them with it. While they were still bewildered, an alien appeared before them. He was a Bravian, an officer of the Space Police Organization tasked with maintaining peace and order across the universe. He explained that he was being targeted by vicious aliens from the Space Prison Sargasso. He also told them he had provided them with a battle machine called "Dag Beagle," created by copying Earth's machines, so they could fight against Sargasso.
Through the Bravian's power, they transformed into Dagwon and battled the space monsters. At that moment, the patrol car drove up in front of En. En merged with the car and became the Brave Robot Dag Fire, defeating the enemy. However, the conflict between the Brave Dagwon and the criminal aliens of Sargasso had only just begun.